Condensate and heat recovery system

ABSTRACT

A trapless condensate and heat recovery system is provided for use with a plurality of parallel connected steam heating coils, each of which is provided with an individual temperature control valve at its inlet side. The coils are connected without the use of traps to a common condensate recovery tank which is provided with pressure and level controls. In one embodiment, the tank is provided with a vent orifice sized to provide adequate venting of noncondensible gases. Alternatively, the tank may be provided with pressure responsive means to bleed off flash steam to a point in a condensate return line from the tank. The condensate return line is coupled either to a deaerating heater or to a makeup storage tank depending on the temperature of the condensate in the line. Live makeup steam is fed into the deaerating heater in response to the pressure within the heater, and excess flash steam within the heater is automatically transferred to the makeup storage tank in response to excess pressure within the heater. In the event that the temperature within the makeup storage tank is excessive, temperature control means responsive to the temperature within the makeup storage tank is employed for controlling an atmospheric vent coupled to the excess steam line to the makeup storage tank. The deaerating heater is provided with level controls to control the feed of water to and from the makeup storage tank.

United States Patent [72] Inventor John S. HamiltonJr.

Monroe, La.

[54] CONDENSATE AND HEAT RECOVERY SYSTEM 23 Claims, 4 Drawing Figs.

[52] US. Cl 237/9 [5 l Int. Cl t F24d 1/02 [50] Field of Search 237/9,67,

[5 6] References Cited UNITED STATES PATENTS 2,055,033 9/1936 Kingsland2,493,365 1/1950 Schramm 2,515,650 7/l950 Hunt et al.

Primary Examiner-Edward J. Michael AttorneyRaphael Semmes Atmosphericout '34 I06 "6 Vent Daoaratlnq I32 I08 ea or '00 as v Make-up WaterABSTRACT: A trapless condensate and heat recovery system is provided foruse with a plurality of parallel connected steam heating coils, each ofwhich is provided with an individual temperature control valve at itsinlet side. The coils are connected without the use of traps to a commoncondensate recovery tank which is provided with pressure and levelcontrols. In one embodiment, the tank is provided with a vent orificesized to provide adequate venting of noncondensible gases.Alternatively, the tank may be provided with pressure responsive meansto bleed off flash steam to a point in a condensate return line from thetank. The condensate return line is coupled either to a deaeratingheater or to a makeup storage tank depending on the temperature of thecondensate in the line. Live makeup steam is fed into the deaeratingheater in response to the pressure within the heater, and excess flashsteam within the heater is automatically transferred to the makeupstorage tank in response to excess pressure within the heater. In theevent that the temperature within the makeup storage tank is excessive,temperature control means responsive to the temperature within themakeup storage tank is employed for controlling an atmospheric ventcoupled to the excess steam line to the makeup storage tank. Thedeaerating heater is provided with level controls to control the feed ofwater to and from the makeup storage tank.

To other 30 From other Heaters Heaters Live Steam Make-up 4 42 Steam 64Supply 56 IZO 9 96 Make-up Storage Tank 94 l j Condensate 88 62 6o Reieiling CONDENSATE AND HEAT RECOVERY SYSTEM BACKGROUND OF THE INVENTIONThis invention relates to steam systems and, more particularly, to acondensate andheat recovery system therefor.

In systems of the prior art employing a plurality of steam heating unitsin parallel, it has been customary to provide each unit with anindividual trap to pass condensate but to prevent the passage of steam.In such systems, there is a tendency for air to become trapped in theunits and interfere with proper heating by the steam. Such systems alsoprovide nonuniform heating and tend to require a considerable length ofstarting time after a shutdown because of the time required for thetraps to pass condensate and for air in the units to work its way out.

There have been a number of proposals in the prior art of steam heatingsystems in which parallel connected steam heat ing units do not employsteam traps. However, it has been difficult to provide efi'ectiv'econtrol of such systems. There is a tendency for steam to appear in thecondensate recovery and return equipmentmaking it difficult to preventthe loss of condensate and heat. Noncondensible gases which causecorrosion have not been disposed of efiectively. The heat output of theheating units has usually been constant rather than controlled.

SUMMARY OF THE INVENTION It is a further object of the invention toprovide meansfor relieving noneondensible gases, which have a tendencyto produce or cause corrosion, at a point near the admission ofcondensate to the system.

It is an additional object of the invention to provide a traplesscondensate and heat recovery system with control of the discharge'ofcondensate to a tank in which complete and final deaeration to levelsacceptable to the industry are maintained for all conditions foroperation.

It is another object of the invention to provide a trapless condensateand heat recovery system with maximum recovery of the heat from thecondensate consistent with overall operating requirements andconditions.

Another object of the invention is the provision of a traplesscondensate and heat recovery system in which loss of condensate isprevented within limits consistent with continuous operation andprotection of piping and equipment.

Still another object of the invention is to provide an automatedtrapless condensate and heat recovery system.

Yet another object of the invention is the provision of a traplesscondensate recovery system witha plurality of parallel connected steamheating coils each of which is individually controlled by the provisionof a temperature responsive control valve at its inlet side.

Briefly, the invention contemplates the provision of a plurality ofsteam heating coils connected in parallel with a common steam supply,each of the heating coilsbeing provided with an individual control valveon its inlet side. Trapless connections are provided from the heatingcoils to a common condensate recovery tank which includes means forcontrolling the pressure within the tank as some of the condensatereceived from the coils flashes to steam. This means may take the formof a vent orifice sized to provide adequate venting of noncondensiblegases and may also include a high condensate level sensing device toclose the valve in response to a high condensate level within the tankto prevent loss of condensate for surge loads or startup operation. Inanother embodiment, the pressure within the tank is controlled bypressure sensing means to bleed off flash steam to a point in acondensate return line from the tank. In addition, the tank is providedwith means to maintairi the level of condensate within the tank constantby controlling a-valve in the condensate return line. Alternatively, apump may be provided in the return line and be associated with arecirculation line and recirculation orifice for returning a portion ofthe pump flow to the condensate receiving tank to avoid flashing in thepump when the valve in the condensate return line is closed. Thecondensate in the return line is fed either, to a deaerating feedwaterheater or to a makeup water storage tank, depending upon the temperatureof condensate within the return line. The pressure within the deaeratingheater is maintained constant by controlling the feed of live steam tothe heater in response to the pressure therein. If excess flash steam isdeveloped in the heater, a pressure controller controls a valve to feedexcess steam to the makeup storage tank. If the temperature within themakeup storage tank is excessive, a temperature controller, responsiveto the temperature in the makeup storage tank, controls a valve from theexcess steam line to an atmospheric vent. Level controls are providedfor feeding makeup water from the storage tank to the deaerating heaterin the event that the level falls or, in the event that the level isexcessive, to return water' from the deaerating heater to the makeupstorage tank. In addition, a level sensor senses the level in the makeupstorage tank to supply makeup water from a water supply source asneeded. Water is returned from the deaerating heater to the boilerswhich supply steamto the system.

Theforegoing and other objects, advantages, and feature of the inventionand the manner in which the same are accomplished will become morereadily apparent from the following detailed description of theinvention when taken in conjunction with the accompanying drawings,which illustrate preferred and exemplary embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic diagram of acondensate and heat recovery system of the invention;

FIG. 2 is a cross section view of a structural detail of the invention;

FIG. 3 is a partial schematic diagram showing an embodiment of theinvention; and

FIG. 4 is a partial schematic diagram showing another embodiment of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning to FIG. 1, itwill be seen that a steam heating system employing the condensate andheat recovery system of the invention includes a steam supply line 10which provides steam from a steam supply, which typically will be one ormore boilers (not shown). Steam from steam supply line It) is suppliedtoa plurality of steam heating coils 12, I4 and I6 connected in parallel.Although three coils are shown, any number might be employed. Each ofthe steam heating coils is provided with an individual control valve onits inlet side.

As shown in FIG. I, steam flows from steam supply header 10 into coil 12through a control valve 18, into coil 14 through a control valve 20, andinto coil 16 through a control valve 22. These valves may be on-offvalves, but more accurate control is obtained when modulating controlvalves are employed. In either event, the valves are controlled inresponse to the temperature in the space, device or process receivingheat from the corresponding coil. To this end, temperature sensors 24,

26 and 28 are positioned so as to monitor the temperature in the space,device or process supplied with heat by coils l2, l4 and 16,respectively, and provide control signals through temperaturecontrollers 30, 32 and 34 to control the corresponding valves 18, 20 and22. When modulating control valves are used, a signal from a temperaturecontroller would continue to force the corresponding valve open, ifsuflicient heat were not supplied with the valve opening initiallycalled for by the temperature controller. In the case of a coil filledwith condensate, there is little heat transfer to further condense thesteam: and with a small valve opening, the steam would generate enoughpressure to remove the condensate. In order to permit condensate to beforced out, as steam is introduced into the heating coils, and not beforced back into adjacent coils, check valves 36, 38 and 40arerespectively provided at the outlet sides of heating coils 12, 14 and16. It is to be noted that the steam traps which are conventionallyemployed in this location have been omitted. Instead, the check valvesdirectly lead to a common condensate receiving header 42.

The header 42 conducts condensate received from the heating coils to acondensate receiving tank 44. Upon entering tank 44, some of thecondensate will flash to steam. This steam is vented with noncondensiblegases through a vent orifice 46. As shown more clearly in FIG. 2,orifice 46 is connected at the end of a pipe 48 leading from tank 44 andcomprises a fitting 50, having a tapered passageway 52 terminating inthe orifice opening 54. This opening is sized for the particularapplication to provide adequate venting of noncondensible gases and toprovide a control of pressure in tank 44 at a level consistent with therequirements for returning the balance of the condensate to the heatrecovery equipment, which will be presently described.

A constant level of condensate water is maintained in condensatereceiving tank 44. This is accomplished by employing some conventionalform of level sensor coupling 56, which may include a pair of levelsensing connections. for transferring the level to a level sensor andcontroller 58 which serves to control the position of level controlvalve 60. Valve 60 is located in the condensate return line 62 leadingfrom tank 44. When the condensate level in tank 44 becomes too high assensed by level coupling 56, controller 58 will provide a signal causingvalve 60 to open. On the other hand, if the condensate level as sensedby sensor coupling 56 falls below the desired level, controller 58 willprovide a signal to close valve 60. In this way, the level within tank44 will be maintained substantially constant.

There is a possibility that some condensate may be lost through orifice46 when the system is started up or in response to surge loads. In orderto prevent this condensate loss, a high level control 64 is employed forsensing a sudden high condensate level, which appears too rapidly foradequate control by controller 58. The controller 64 provides a signalto operate a vent control valve 66 closing vent 46 in the presence ofthese unusually high surges to prevent condensate from passing throughorifice 46.

In another embodiment as illustrated in FIG. 3, the pressure withinreceiving tank 44 may be controlled by providing a pressure sensingconnection 68 and an associated pressure controller 70 for controllingthe opening of a pressure control valve 72 located in a bleed line 74.As will be seen from FIG. 3, bleed line 74 feeds into condensate returnline 62 at a point downstream from level control valve 60. In this way,flash steam within tank 44 which causes the pressure within tank 44 tobe excessive may be bled off to return line 62 to reduce the pressurewithin tank 44.

Although, as shown in FIGS. 1 and 3, condensate from receiving tank 44is fed through valve 60 directly into condensate return line 62, it issometimes desirable to provide power means for discharging thecondensate from the receiving tank. If, for example, it is desired topump the condensate directly to a steam boiler, a pump may be needed toaugment the pressure. Thus, as shown in FIG. 4, a pump 76 is placed incondensate return line 62 at a point upstream of level control valve 60.This pump will provide a higher discharge pressure than is obtainablefrom the receiving tank 44 directly, and this discharge pressure willnow be sufficient to return the condensate to any point desired. Arecirculation line 78, including a recirculation orifice 80, is providedto return a portion of the pump flow to receiving tank 44 in order toavoid flashing in the pump when control valve 60 is in its closedposition.

Returning to FIG. 1, it will be seen that condensate in condensatereturn line 62 will be fed either to a deaerating feedwater heater 82 orto a makeup water storage tank 84. It may happen during startup of thesteam heating system, or because one or more of the units of the systemhad been cooled to a very low temperature, that the temperature of thecondensate leaving the receiving tank 44 will be below that allowingsatisfactory operation for a given operating pressure in the deaeratingheater 82. It has been found, for example, in a particular system, thatcondensate temperatures below 230 F. would not be acceptable withindeaerating feedwater heater 82. Thus, the present system is providedwith a temperature controller 86 for sensing the temperature ofcondensate in condensate return line 62 to develop a control signal forcontrolling a three-way valve 88. In addition, a thermometer 90 may beprovided so that the temperature of the condensate may be monitored.When the temperature of the condensate drops below the acceptable levelfor the heater pressure, temperature controller 86 will actuatethree-way valve 88 to allow condensate to return directly to makeupstorage tank 84 through a perforated pipe 92 contained therein. Thecondensate water will then be returned to the deaerating heater 82through a makeup water pump 94 connected in a makeup pump line 96through a deaerating heater level control valve 97. In order to avoidflashing within pump 94. a recirculation line 98, containing arecirculation orifice 99, is provided to return some of the output frompump 94 to makeup storage tank 84 in the event that valve 97 is closed.However, when the temperature of the condensate in condensate returnline 62 is above the acceptable level, temperature controller 86 willactuate valve 88 to return all of the condensate directly to deaeratingheater 82.

Deaerating heater 82 has the principal function of removing allnoncondensible gases from water to be used for boiler feed. It isnecessary that the pressure within deaerating heater 82 be maintainedconstant. To this end, a pressure controller 100 senses the pressurewithin the deaerating heater 82 and develops a control signal forcontrolling a valve 102 which regulates the feed of live steam from alive steam makeup line 104 connected to a source (not shown) of highpressure steam into deaerating heater 82. In this way, sufficient steamis fed into deaerating heater 82 to maintain the pressure thereinconstant. Noncondensible gases will be vented through vent 106, the flowthrough which may be controlled by a manual vent valve 108.

When the system is operating under normal conditions, the hightemperature condensate being returned to deaerating heater 82 will be ata temperature above the saturation temperature at the pressure withinthe heater. This will cause at least some of the condensate enteringheater 82 to flash to steam with a consequent reduction of thecondensate temperature to the operating temperature of the deaeratingheater. The effect of the flash steam is to provide necessary additionalheat to makeup water supplied to the deaerating heater from makeupstorage tank 84 through valve 97. Since the additional steam withindeaerating heater 82 will raise the pressure therein, pressurecontroller I00 will then reduce or shut off the supply of live steamthrough live steam makeup valve 102. At times the flash steam providedmay exceed the steam requirement for heating the incoming makeup water.The pressure in deaerating heater 82 will rise to, first, cause shutoffof valve 102 by operation of pressure controller 100; and then, at aslightly higher pressure, excess steam will be relived through an excesssteam control valve 114 which is controlled by a pressure controller 116responsive to excessive pressure within deaerating heater 82. The excesssteam is fed to makeup storage tank 84 through an excess steam line 118which is connected to the perforated pipe 92 at an end opposite to theend connected to valve 88.

A constant condensate level is maintained in deaerating heater 82 byproviding a level sensor coupling which develops a control signal inlevel controller 112 for operating level control valve 97. Thus, makeupwater from makeup storage tank 84 will be admitted through valve 97 onlywhen the condensate level within heater 82 drops below a predeterminedlevel as sensed by level sensor coupling 0.

A constant level is maintained in makeup storage tank 84 by providing alevel sensor coupling 120 for developing a signal in a level controller122. This signal is employed for controlling a makeup water valve 124connected in a makeup water line 126 which may be connected to a coldwater supply supplied under pressure from a community water supply,well, reservoir or other source which might be available.

In the event that the amount of excess steam returned through excesssteam return line 118 is sufiicient to heat the water in makeup storagetank 84 to a temperature in excess of the maximum allowable temperaturein makeup water pump 94, a temperature sensor 128 causes a temperaturecontroller 130 to provide a control signal opening an atmospheric ventvalve 132 leading to an atmospheric vent 134 from excess steam line 118.Excess steam will thus be relieved to the atmosphere. A thermometer 129may be provided to monitor the temperature in tank 84.

Condensate accumulating in deaerating heater 82 is returned to one ormore steam boiler or boilers through a boiler return line 142. in orderto assist this return and to insure that it is at adequate pressure, aboiler return pump 144 is provided in boilenreturn line 142. It is to beunderstood that various controls may be provided further along boilerreturn line 142 to regulate the flow of water returned to the boiler orboilers. In the event that such controls may unduly restrict flow fromdeaerating heater 82 and cause undue pressure within pump 144, arecirculation line 146, having a recirculation orifice 148, is providedforreturning some of the flow from pump 144 to deaerating heater 82. I

At times, the volumes of condensate returning from the system to theboiler or boilers may exceed the amount required for operation of theboiler or boilers. The level in deaerating heater 82 may then rise to apoint at which all incoming makeup water is shut off by controller 112and above an overflow level. An overflow controller or trap 136 willthen open to allow return of excess condensateto makeup storage tank 84through a condensate return pipe v138 to pipe 140 discharging below thenormal water line or through perforated pipe 92.

It is believed that the operation of the system just described will bereadily apparent. A system of this character has been employed forheating dry kilns of the type employed in sawmill operations and hasbeen operated very satisfactorily in this application.

While preferred embodiments of the invention have been shown anddescribed, it will be apparent to those skilled in the art that changescan be made without departing from the principles and spirit of theinvention, the scope of which is defined in the appended claims. Forexample, instead of employing pressure controller 100, the feed of livesteam through valve 1102 might be controlled by means of a temperaturesensing element, located within the water storage area of heater 82below the water level, and temperature controller. Accordingly, theforegoing embodiments are to be considered illustrative rather thanrestrictive of the invention, and those modifications which come withinthe meaning and range of equivalency of the claims are to be includedtherein.

lclaim: 1. A steam heating system comprising: a plurality of steamheating coils connected in parallel with a common steam supply, each ofsaid heating coils having an individual condition responsive controlvalve on its inlet side;

trapless means for connecting said heating coils to a common condensaterecovery tank to feed condensate forced by steam from said coils andsaid tank, said means being unregulated in the direction of flow to saidtank;

means for controlling the pressure within said tank as some of saidcondensate received from said coils flashes to steam; and

means to maintain the level of condensate within said tank substantiallyconstant.

2. A steam heating system as recited in claim l,wherein said means forcontrolling pressure within said tank comprises a vent orifice sized toprovide adequate venting of noncondensible gases and to control thepressure within said tank at a level consistent with the return ofcondensate from said tank to heat recovery equipment of said system.

3. A steam heating system comprising: a plurality of steam heating coilsconnected in parallel with a common steam supply, each of said heatingcoils having an individual condition responsive control valve on itsinlet side; trapless means for connecting said heating coils to a commoncondensate recovery tank to feed condensate forced by steam from saidcoils to said tank; means for controlling the pressure within said tankas some of said condensate received from said coils flashes to steam;and

means to maintain the level of condensate within said tank substantiallyconstant, said means for controlling pressure within said tank'furthercomprising a vent control valve and high condensate level sensing meansto close said valve in response to a high condensate level within saidtank to prevent loss of condensate for surge loads or startup operation.4. A steam heating system as recited in claim 1 wherein said means forcontrolling pressure within said tank comprises pressure sensing meansand valve means responsive to said pressure sensing means to bleed offflash steam to a point in a condensate return line from said tank.

5. A steam heating system as recited in claim 1 wherein said means tomaintain the level of condensate within said tank constant comprisesmeans for sensing the level of condensate within said tank, a condensatereturn line from said tank, and level control valve means in saidcondensate return line responsive to said means for sensing the level ofcondensate withinlsaid tank.

6. A steam heating system comprising: a plurality of steam heating coilsconnected in parallel with a common steam supply, each of said heatingcoils having an individual condition responsive control valve on itsinlet side;

trapless means for connecting said heating coils to a common condensaterecovery tank to feed condensate forced by steam from said coils to saidtank; means for controlling the pressure within said tank as some ofsaid condensate received from said coils flashes to steam; and I meansto maintain the level of condensate within said tank substantiallyconstant, said means to maintain the level of condensate within the tankconstant comprising means for sensing the level of condensate withinsaid tank, a condensate return line from said tank, level control valvemeans in said condensate return line responsive to said means forsensing the level of condensate within said tank, a pump in said returnline at a point upstream from said level control valve means, and arecirculation line in cluding a recirculation orifice for returningaportion of the pump flow to said condensate receiving tank to avoidflashing in said pump when said level control valve means is closed. 7.A steam heating system comprising: a plurality of steam heating coilsconnected in parallel with a common steam supply, each of said heatingcoils having an individual condition responsive control valve on itsinlet side;

trapless means for connecting said heating coils to a common condensaterecovery tank to feed condensate forced by steam from said coils to saidtank;

means for controlling the pressure within said tank as some of saidcondensate received from said coils flashes to steam; I

means to maintain the level of condensate within said tank substantiallyconstant;

a return line from said condensate recovery tank;

a deaerating feedwater heater;

a makeup water storage tank; and

control valve means responsive to the temperature of condensate withinsaid return line for feeding condensate from said return line to saidmakeup storage tank when said temperature is below a predetermined valueand to said deaerating heater when said temperature exceeds saidpredetermined value.

8. A steam heating system as recited in claim 7, further comprisingmeans to maintain a constant pressure in said deaerating heater.

9. A steam heating system as recited in claim 8 wherein said means tomaintain a constant pressure in said deaerating heater comprises meansfor sensing the pressure within said deaerating heater and means,including a valve responsive to said means for sensing the pressurewithin said heater, for feeding live steam from a high pressure sourceinto said heater.

10. A steam heating system as recited in claim 9 wherein said deaeratingheater includes heater level sensing means and a control valveresponsive to said heater level sensing means for feeding makeup waterfrom said makeup storage tank.

H. A steam heating system as recited in claim 10, wherein saiddeaerating heater includes means responsive to pressure within saidheater to relieve excess steam, flashed from high temperature condensateentering said heater, through a valve to the makeup storage tank.

12. A steam heating system as recited in claim 11, wherein said excesssteam is fed to a perforated pipe within said makeup storage tank toheat the water stored therein.

13. A steam heating system as recited in claim 11, wherein said makeupstorage tank includes means to maintain a constant water level thereinby controlling a supply of makeup water thereto.

14. A steam heating system as recited in claim 11, further comprisingmeans responsive to excess temperature within said makeup storage tankfor venting said excess steam to atmosphere.

15. A steam heating system as recited in claim 7. wherein saiddeaerating heater includes excess level responsive means to returncondensate to said makeup storage tank.

16. A steam heating system as recited in claim I. wherein saidindividual control valves are responsive to a temperature condition inthe space'affected by its corresponding heating coil.

17. A steam heating system comprising:

a return line for returning condensate from said system;

a deaerating feedwater heater;

a makeup water storage tank; and

valve means responsive to the temperature of said condensate in saidreturn line for feeding condensate from said return line to said makeupstorage tank when said temperature is below a predetermined value and tosaid deaerating heater when said temperature exceeds said predeterminedvalue.

18. A steam heating system as recited in claim 17 wherein saiddeaerating heater includes means responsive to the pressure therein forfeeding steam under pressure thereto.

19. A steam heating system as recited in claim l8 wherein said heaterincludes level responsive means for feeding makeup water from saidmakeup tank to said heater.

20. A steam heating system as recited in claim 19, wherein meansresponsive to pressure within said heater relieves excess flash steam tosaid tank.

21. A steam heating system as recited in claim 20 wherein said excesssteam is fed to one end of a perforated pipe within said tank, the otherend of said pipe being connected to said valve means.

22. A steam heating system as recited in claim 20, further comprisingmeans responsive to excess temperature within said tank for venting saidexcess steam to atmosphere.

23. A steam heating system as recited in claim [9. further comprisingmeans responsive to overflow of condensate within said heater forreturning condensate to said tank.

1. A steam heating system comprising: a plurality of steam heating coilsconnected in parallel with a common steam supply, each of said heatingcoils having an individual condition responsive control valve on itsinlet side; trapless means for connecting said heating coils to a commoncondensate recovery tank to feed condensate forced by steam from saidcoils and said tank, said means being unregulated in the direction offlow to said tank; means for controlling the pressure within said tankas some of said condensate received from said coils flashes to steam;and means to maintain the level of condensate within said tanksubstantially constant.
 2. A steam heating system as recited in claim 1,wherein said means for controlling pressure within said tank comprises avent orifice sized to provide adequate venting of noncondensible gasesand to control the pressure within said tank at a level consistent withthe return of condensate from said tank to heat recovery equipment ofsaid system.
 3. A steam heating system comprising: a plurality of steamheating coils connected in parallel with a common steam supply, each ofsaid heating coils having an individual condition responsive controlvalve on its inlet side; trapless means for connecting said heatingcoils to a common condensate recovery tank to feed condensate forced bysteam from said coils to said tank; means for controlling the pressurewithin said tank as some of said condensate received from said coilsflashes to steam; and means to maintain the level of condensate withinsaid tank substantially constant, said means for controlling pressurewithin said tank further comprising a vent control valve and highcondensate level sensing means to close said valve in response to a highcondensate level within said tank to prevent loss of condensate forsurge loads or startup operation.
 4. A steam heating system as recitedin claim 1 wherein said means for controlling pressure within said tankcomprises pressure sensing means and valve means responsive to saidpressure sensing means to bleed off flash steam to a point in acondensate return line from said tank.
 5. A steam heating system asrecited in claim 1 wherein said means to maintain the level ofcondensate within said tank constanT comprises means for sensing thelevel of condensate within said tank, a condensate return line from saidtank, and level control valve means in said condensate return lineresponsive to said means for sensing the level of condensate within saidtank.
 6. A steam heating system comprising: a plurality of steam heatingcoils connected in parallel with a common steam supply, each of saidheating coils having an individual condition responsive control valve onits inlet side; trapless means for connecting said heating coils to acommon condensate recovery tank to feed condensate forced by steam fromsaid coils to said tank; means for controlling the pressure within saidtank as some of said condensate received from said coils flashes tosteam; and means to maintain the level of condensate within said tanksubstantially constant, said means to maintain the level of condensatewithin the tank constant comprising means for sensing the level ofcondensate within said tank, a condensate return line from said tank,level control valve means in said condensate return line responsive tosaid means for sensing the level of condensate within said tank, a pumpin said return line at a point upstream from said level control valvemeans, and a recirculation line including a recirculation orifice forreturning a portion of the pump flow to said condensate receiving tankto avoid flashing in said pump when said level control valve means isclosed.
 7. A steam heating system comprising: a plurality of steamheating coils connected in parallel with a common steam supply, each ofsaid heating coils having an individual condition responsive controlvalve on its inlet side; trapless means for connecting said heatingcoils to a common condensate recovery tank to feed condensate forced bysteam from said coils to said tank; means for controlling the pressurewithin said tank as some of said condensate received from said coilsflashes to steam; means to maintain the level of condensate within saidtank substantially constant; a return line from said condensate recoverytank; a deaerating feedwater heater; a makeup water storage tank; andcontrol valve means responsive to the temperature of condensate withinsaid return line for feeding condensate from said return line to saidmakeup storage tank when said temperature is below a predetermined valueand to said deaerating heater when said temperature exceeds saidpredetermined value.
 8. A steam heating system as recited in claim 7,further comprising means to maintain a constant pressure in saiddeaerating heater.
 9. A steam heating system as recited in claim 8wherein said means to maintain a constant pressure in said deaeratingheater comprises means for sensing the pressure within said deaeratingheater and means, including a valve responsive to said means for sensingthe pressure within said heater, for feeding live steam from a highpressure source into said heater.
 10. A steam heating system as recitedin claim 9 wherein said deaerating heater includes heater level sensingmeans and a control valve responsive to said heater level sensing meansfor feeding makeup water from said makeup storage tank.
 11. A steamheating system as recited in claim 10, wherein said deaerating heaterincludes means responsive to pressure within said heater to relieveexcess steam, flashed from high temperature condensate entering saidheater, through a valve to the makeup storage tank.
 12. A steam heatingsystem as recited in claim 11, wherein said excess steam is fed to aperforated pipe within said makeup storage tank to heat the water storedtherein.
 13. A steam heating system as recited in claim 11, wherein saidmakeup storage tank includes means to maintain a constant water leveltherein by controlling a supply of makeup water thereto.
 14. A steamheating system as recited in claim 11, further comprising meansresponsive to excess temperature within said makeup storage taNk forventing said excess steam to atmosphere.
 15. A steam heating system asrecited in claim 7, wherein said deaerating heater includes excess levelresponsive means to return condensate to said makeup storage tank.
 16. Asteam heating system as recited in claim 1, wherein said individualcontrol valves are responsive to a temperature condition in the spaceaffected by its corresponding heating coil.
 17. A steam heating systemcomprising: a return line for returning condensate from said system; adeaerating feedwater heater; a makeup water storage tank; and valvemeans responsive to the temperature of said condensate in said returnline for feeding condensate from said return line to said makeup storagetank when said temperature is below a predetermined value and to saiddeaerating heater when said temperature exceeds said predeterminedvalue.
 18. A steam heating system as recited in claim 17 wherein saiddeaerating heater includes means responsive to the pressure therein forfeeding steam under pressure thereto.
 19. A steam heating system asrecited in claim 18 wherein said heater includes level responsive meansfor feeding makeup water from said makeup tank to said heater.
 20. Asteam heating system as recited in claim 19, wherein means responsive topressure within said heater relieves excess flash steam to said tank.21. A steam heating system as recited in claim 20 wherein said excesssteam is fed to one end of a perforated pipe within said tank, the otherend of said pipe being connected to said valve means.
 22. A steamheating system as recited in claim 20, further comprising meansresponsive to excess temperature within said tank for venting saidexcess steam to atmosphere.
 23. A steam heating system as recited inclaim 19, further comprising means responsive to overflow of condensatewithin said heater for returning condensate to said tank.